The invention relates generally to the field of teletherapy and in particular to a system and method for identifying a patient location within a treatment room utilizing a scout image of a computerized tomography scanner.
Teletherapy is defined as a treatment methodology in which an irradiation source is at a distance from the body to be treated. X-rays and electron beams have long been used in teletherapy to treat various cancers. Unfortunately, X-rays and electron beams exhibit a linear energy transfer approaching an exponential attenuation function, and are therefore of minimal use for deeply embedded growths. Recently, the use of heavy particles, particularly hadrons, in teletherapy has found increasing acceptance, due to the ability of heavy particles to penetrate to a specific depth without appreciably harming intervening tissue. In particular, the linear energy transfer of hadrons exhibits an inversed depth profile with a marked Bragg peak defined as the point at which the hadrons deposit most of their energy, and occurs at the end of the hadrons path. As a result of this effect, increased energy can be directed at an embedded growth as compared to X-rays and electron beams, which particularly harm intervening tissues. While the term hadrons include a wide range of particles, practically, protons and various ions are most widely used in therapy.
Pre-treatment imaging is an important part of teletherapy and is particularly important in obtaining precise location information of the patient as well as updated information regarding the diseased tissue to be irradiated. Location information of the patient is required for accurate positioning of the patient in relation to the irradiation beam.
Prior art methods of pre-treatment imaging exist based on x-ray technology, wherein an x-ray image, or a pair of orthogonal x-ray images, is taken of an immobilized patient in position for irradiation. The x-ray image, or a pair of orthogonal images, is compared with synthetic x-ray images derived from a reference computerized tomography (CT) scan used for initial treatment planning, and any location adjustments are performed. The synthetic x-ray image is often called a digital reconstructed radiograph (DRR).
Commercially available CT units are typically arranged to display or otherwise output a scout image, wherein the CT unit provides a quickly acquired x-ray projection, which is used in the prior art to both prescribe desired CT slices, and/or to provide a complete three dimensional image of a selected area, which is typically finely selected responsive to the scout image. Thus a scout image is a planar image or a curved-planar image of a patient created by a CT unit. CT units provide scout images based on a number of scout generation technologies, including, but not limited to: a moving fan-beam shaped single detector row geometry; a single static fan-beam shaped multi-detector row geometry; and a moving fan-beam shaped multi-detector row geometry.
An in-room CT, wherein a CT unit is provided within a teletherapy treatment room co-located with teletherapy equipment, has been proposed as providing extremely accurate positioning and continued anatomical volume imaging thus allowing for frequent treatment plan updates. Unfortunately, a CT scan exposes the patient to a very large radiation dose, which is not desirable on a regular basis. Furthermore a CT scan is time consuming and thus reduces the throughput of the teletherapy treatment room.
The layout of a teletherapy treatment room is a major expense, and the equipment required for proper operation must be selected and carefully placed so as to maximize throughput. In particular, any equipment utilized in identifying precise patient location must be arranged to be at known coordinates, or at a controlled range of coordinates, in relation to the irradiation source.